1. Field of the Invention
The invention relates to a semiconductor device constructed by arranging a plurality of light emitting elements and relates to a print head comprising the semiconductor device and an image forming apparatus comprising the print head.
2. Related Background Art
FIG. 13 is a diagram showing a structure of conventional LED head as a print head using LED serving as light emitting element.
As shown by the FIG. 13, in a LED head 219 furnished in a printer that is able to perform a print on paper of e.g. A4 size and has a resolution of 600 dots per inch, a print data signal HD-DATA is inputted to the LED head 219 together with a clock signal HD-CLK, and bit data of 4992 dots are sequentially send to a shift register circuit composed of flip-flop circuits of FF1, FF2, . . . , FF4992.
Next, in the LED head 219, when a latch signal HD-LOAD is inputted to the LED head 219, the bit data are latched by respective latch circuits of LT1, LT2, . . . , LT4992. Continuously, in the LED head 219, through the bit data and a print drive signal HD-STB-N, in the light emitting elements of LD1, LD2, . . . , LD4992, these light emitting elements corresponding to dot data with high level emit light. Moreover, G0 is an inverter circuit; G1, G2, . . . , G4992 are pre-buffer circuits; Tr1, Tr2, . . . , Tr4992 are switch elements; and VDD is a power source (for example, refer to Patent document 1).
Patent document 1: Japan patent publication H2-263668.
However, the above-stated conventional LED head comprises a great many LEDs, and each LED is connected with a transistor in which strong drive electricity corresponding to drive ability flows. Though the LED may simplify the structure of its own so as to reduce electricity for emitting light, it is necessary to make strong drive electricity flow into the transistor in order to drive the LED. Thus, there are such problems: the drive element such as the transistor and the like becomes large-scale, so it possesses a larger chip area, and the cost of the drive element rises.